Time-resolved measurements of HO2 and OH have been conducted in 355 nm photolysis of dimethyl ether/Cl-2/O-2 mixture at elevated temperature, using near-infrared frequency modulation spectroscopy. A part of OH was found to be produced at a timescale of several microseconds by the methoxymethyl with O-2 reaction, while HO2 is formed mainly in milliseconds with the yield increasing up to 60% between 500 and 600 K. It was rationalized that HO2 is not a direct product of the 02 adduct decomposition, but a secondary product through HCHO + OH reaction. Another pathway through HCO formation from the adduct is also discussed. (c) 2006 Elsevier B.V. All rights reserved.